Phone apps aren't nearly as good as dedicated measurement systems. Think about it: The phone application developer has no way of knowing what quality the microphone or input circuitry is like, so the system cannot be calibrated. Phone measurement apps are gimmicky, at least at this time. One could calibrate the hardware though, so those kinds of apps could potentially become more accurate at some point.
I had no idea there were any such apps. As you have mentioned, I don't think they are at that place where they can be fully relied upon.
Perhaps in the future, we'll have more accurate and reliable systems.